The diet proposes that consuming less acidic foods and beverages makes a person more healthy, prevents ageing and helps with weight loss.

“There really is no evidence that supports the idea that eating in this way has any healthy benefits,” Caulfield told INSIDER. “To make your diet more complicated based on something that doesn’t have science to support it isn’t a great idea.”

An alkaline diet entails cutting out meat, wheat dairy, refined sugars and other foods deemed high in acid, according to Caulfield.

Alkaline diet followers often test the acidity in their urine, believing it to be an indicator of their body’s pH balance. In fact, MacPherson recently told the London Evening Standard that she carries a pH balance tester urine kit in her purse at all times to check that she’s in an alkaline state.

But, the pH levels in a person’s urine are entirely different from the pH levels in the rest of their body, according to Caulfield. Furthermore, what a person eats has the potential to affect the acidity of their urine — but not their body.

“There’s really no evidence that how you eat is going to have a profound impact on the acidity of your actual body. Some of these theories often talk about the acidity of your urine as a marker, but that’s not the acidity of your body; that’s the acidity of your urine. These foods can impact the pH levels of your urine, and not your blood,” Caulfield said.

The scientist says there’s also no proof that the diet actually helps people lose weight. Instead, he suggests that what the diet does is force people to actually think about what they’re eating, which can inspire them to make healthier dietary decisions.

“This is a really common phenomenon, whether you’re talking about gluten-free, Paleo, name the diet,” he said. “What it is, is people pay attention to what they’re eating over a period of time, and it makes them lose weight. Studies show over the long term there’s no special diet that’s better than any other.”

And so, Caulfield urges people to exercise caution when deciding if they should follow the same diet as their favourite celebrity. Oftentimes, whether you’ll end up looking like a supermodel is completely out of your hands.

“The thing that’s really important to do if you want to age gracefully is to pick your parents and have good genetics. Elle obviously did a good job with that latter strategy; she chose some good genes,” Caulfield said.